AnsweredAssumed Answered

External timer clock source

Question asked by Gregorsanec.Toni on Feb 27, 2014
Latest reply on Feb 28, 2014 by Clive One
Hi,

I am trying to use external clock source for TIMER via TIMERx_ETR pin. Timer is counting,
but I it looks like, that this clock is not feed to the timer counter directly and I am experiencing
"bad" time period. My input clock is 32.768000Mhz from high stability TCXO. In this application note:

http://www.st.com/st-web-ui/static/active/en/resource/technical/document/application_note/DM00042534.pdf

is stated:

"
In these cases, the clock is provided by an external signal connected to TIx pins or ETR pin. 
The maximum external clock frequency should be verified.
In addition to all these clock sources, the timer should be clocked with the APBx clock.
The external clocks are not directly feeding the prescaler, but they are first synchronized 
with the APBx clock through dedicated logical blocks.
"


So the questions are:
Is my external clock too high?
External clock is somehow discharged and timer is clocked from internal clock after
synchronization taken place.

Could someone please explain this situation.

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